METHOD AND ARRANGEMENT FOR MEASURING THE CONDITION OF A BASE STATION

Abstract: The invention relates to a method for measuring the condition of a receiving antenna of a base station in a TDMA radio system, in which TDMA channel structures according to ETSI/GSM recommendation 05.02 are used, by means of test measurements performed in predetermined TDMA time slots. According to the invention, the test measurements are performed, without disturbing the normal operation of the base station and without allocating a traffic channel, during time slots of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or during time slots of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02.

Description: Method and arrangement for measuring the condition of a base station The invention relates to a method and arrange- ments for measuring the condition of a base station in a TDMA radio system, in which are used TDMA channel structures according to ETSI/GSM recommendation 05.02, by means of test measurements performed in predetermined TDMA time slots. One of the most critical factors in radio sys¬ tems, for instance in cellular radio telephone systems, is the quality of a radio link between a base station and a mobile radio station. The quality of this radio link is essentially affected by the condition of radio sections of the base station, i.e. antennas and trans¬ ceivers. Therefore, it is important to be able to moni¬ tor the condition of the radio sections of the base station by various measurements and tests. The condition of the transmitting and receiving antennas of a base station is typically monitored by measuring the standing wave ratio thereof, i.e. electri¬ cal matching of the antennas to the remaining part of the receiver and transmitter system. This has normally been performed by means of an equipment positioned at the base station, supplying RF power through an antenna line to the antenna and measuring the power reflected from the antenna. The condition of the antenna has been concluded from the level of the signal reflected from the antenna. The measurements are usually carried out at a specific test frequency outside the normal operat¬ ing frequency band of the base station, in order to avoid disturbance to the normal operation of the base station. Some equipments applying this principle are described in the Finnish Patent Application 904085 as well as in the European Patent Application 0 261 828. The condition of transceivers as well as base¬ band signal processing units of a base station have been tested by an equipment looping an RF test signal sent by a transmitter to a receiver. If the sent test signal is received error free, the devices to be tested are assumed to be in a proper condition. In digital radio systems, it is possible to calculate on the basis of a comparison between transmitted and received data a Bit Error Rate (BER), which is below a predetermined limit value at a base station in a proper condition. The radio test equipment is typically connected between transmit¬ ting antenna line and receiving antenna line and it has to convert the test signal from transmission frequency to reception frequency. Some equipments of this type are described in the Finnish Patent Application 902624 and in the PCT Application WO90/06635. New digital radio systems of TDMA (Time Divi¬ sion Multiple Access) type have time-division signalling including several, typically 8, time slots at one fre- quency. One TDMA system is the Pan-European mobile tele¬ phone system GSM. Also in the digital radio systems, the test measurements have to be carried out at frequencies outside the normal frequency band of the base station, if it is not desirable to disturb the normal operation of the base station. If normal frequencies of the base station are desired to be used for the test measurements performed during the operation of the base station, it is necessary to remove one of the time slots from the "normal traffic" for test use. For this reason, a con- tinuous monitoring of the radio sections of the base station and real-time alarms have not been possible. One object of the invention is to implement a measurement of the condition of an antenna at frequen¬ cies actually used at a base station of a TDMA radio system without disturbing the normal operation of the base station. This is achieved by means of a method of the type disclosed in the preamble, which method is accord- ing to the invention characterized in that the test measurements are performed in time slots of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or in time slots of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02. An aspect of,the invention relates also to an arrangement for measuring the condition of a receiving antenna of a base station in a TDMA radio system using TDMA channel structures according to ETSI/GSM recommen¬ dation 05.02, by means of test measurements performed in predetermined TDMA time slots. The arrangement is characterized in that it comprises means for sending a predetermined radio fre¬ quency test signal via an antenna line to the antenna during at least one time slot of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or during at least one time slot of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02, means for measuring the magnitude of a measur¬ ing signal component reflected from the antenna and propagated along a predetermined measuring path, means for sending a measuring signal directly towards a receiver along said measuring path during one or several time slots of said IDLE frame, means for measuring the magnitude of the mea- suring signal sent directly along the measuring path, means for determining the condition of the an¬ tenna on the basis of the ratio of these two measured signal magnitudes. The invention further relates to an arrangement for measuring the condition of a base station in a TDMA radio system using TDMA channel structures according to ETSI/GSM recommendation 05.02, by means of test measure¬ ments performed in predetermined TDMA time slots. The arrangement is characterized in that it comprises means for sending a predetermined radio fre¬ quency test signal to a receiver of the base station on a radio channel during at least one time slot of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or dur¬ ing at least one time slot of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommenda¬ tion 05.02, means for determining a bit error rate on the basis of test data received by the receiver of the base station and known test data. The ETSI/GSM recommendation 05.02 defines the channel structures to be used on the radio path at a radio interface of a GSM system. The channel structure TCH/F+SACCH/TF and the channel structure SDCCH/8 defined in the recommendation comprise at a specific position so-called IDLE frames, the use of which is not defined in any way. In the invention, the desired test measure¬ ments of the base station are performed in one or sev¬ eral time slots of some idle frame, whereby the measure¬ ments do not occupy time slots suitable for other traf- fie. Thus it is possible to monitor the base station continuously during operation by means of the invention, irrespective of the traffic situation and without affec¬ ting the traffic capacity of the base station, due to which it is possible to discover a failure in real time and to generate an alarm. In the following, the invention will be ex¬ plained in greater detail by means of illustrative embo¬ diments referring to the attached drawing, in which Figures 1 and 2 show an allocation of the time slots of two radio channels of a base station between control and traffic channel structures, Figures 3, 4, 5 and 6 illustrate a TDMA frame structure, Figure 7 shows a TCH/F traffic channel struc¬ ture, Figure 8 is a block diagram illustrating a measuring arrangement of a base station according to the invention. , The present invention is suitable for being used for measuring the condition of a receiving antenna of a base station in TDMA radio systems using TDMA chan¬ nel structures according to ETSI/GSM recommendation 05.02. Such systems are the Pan-European mobile communi¬ cation system GSM and direct modifications thereof, such as DCS 1800 (Digital Communication System). For a more detailed description of the GSM sys¬ tem is referred to the ETSI/GSM recommendations and to the book "The GSM System for Mobile Communications", M. Mouly & M-B. Pautet, Palaiseau, France, 1992, ISBN:2- 9507190-0-7. Only features essential for the invention will be discussed separately below. The GSM system follows FDMA (Frequency Division Multiple Access) principle, in which system are used a number of radio channels (carrier wave frequencies). On the other hand, time division multiplexing is applied to the radio channels on TDMA principle in such a way that each radio channel includes several, typically 8, time slots. The time slots are mainly used for carrying control channels (CCH) and traffic channels (TCH). Speech and data are transmitted on the traffic channels. On the control channels, a signalling is performed between a base station and mobile subscriber stations. Figure 1 shows two full-duplex radio channels, each comprising transmission and reception carriers Ful, Fil and Fu2, Fi2, which are spaced apart by a duplex spacing, e.g. 45 MHz. On the first radio channel Ful, Fil, the following channel structures are carried in eight time slots: one common control channel CCH, six traffic channels TCH and one Stand alone Dedicated Con¬ trol Channel SDCCH. On the second radio channel, the traffic channel TCH is carried in each time slot. Chan- nel structures being of interest for the invention are TCH and SDCCH. Firstly, there is, however, reason to study the frame structure of a GSM system in general, which struc¬ ture is illustrated in the figures 3 to 6. Figure 6 shows one TDMA basic frame preferably including eight time slots to be used as traffic and control channels. 26 or 51 successive TDMA frames constitute one multi- frame, depending on whether a traffic or a control chan¬ nel structure is concerned, as is illustrated in Figure 5. On the other hand, a superframe is constituted by 51 or 26 successive multiframes, depending on whether, the multiframes comprise 26 or 51 frames, as is illustrated in Figure 4. Further, a hyperframe is constituted by 2048 superframes, as is illustrated in Figure 3. Alter- natively, one multiframe may contain 26 TDMA frames, whereby one superframe contains 51 multiframes. The ETSI/GSM recommendation 05.02 defines the channel structures to be used on the radio path at a radio interface of a GSM system. Figure 7 illustrates a traffic channel structure TCH/F+SACCH/TF defined in the recommendation, the last frame of the multiframe being a so-called IDLE frame, the use of which is not defined in any way. On each traffic channel TCH of Fig¬ ure 1, for instance, an IDLE frame is thus regularly repeated, without being allocated for any use, not even when the other frames of the traffic channel have an ongoing call. According to the invention, the desired measurements of the radio sections of a base station are carried out in one or several time slots of such an IDLE frame, whereby the test measurements may take place without allocating the traffic channel, and also when the traffic channel has an ongoing call. Corresponding IDLE frames are also found in the channel structure SDCCH/8 defined for the stand alone dedicated control channel SDCCH. When the desired test measurements are performed in these IDLE frames, they do not disturb the normal operation of the control chan¬ nel. According to the invention, the measurements to be performed in the IDLE frames described above may contain any measurements necessary for the base station. A measurement of the condition of a receiving antenna and a measurement of the condition of a receiver will be described as examples in the following. A TDMA transceiver shown in Figure 8 comprises at least two, preferably four, pairs of transceivers 21A, 210A and 21B, 210B, respectively, each pair consti¬ tuting one full-duplex link. The outputs of the trans¬ mitter units 21A and 21B are connected by means of a combining element 22 (combiner) to a common antenna line 23 and to a common transmitting antenna 24. A receiving antenna 26 is connected via an antenna line 27 to a branching element 29 dividing the received signal to the receiver units 210A and 210B. As used herein, transmit- ter and receiver units primarily signify the radio sec¬ tions of a transceiver. The base station further comprises a baseband interface equipment 12 for interfacing the base station to a digital link 11, typically a PCM link, from a base station controller BSC and a mobile telephone exchange MSC. User data and control data received from the link 11 are mapped into TDMA frames of a frame unit 7, chan¬ nel-coded, interleaved and modulated in a transmitter unit 21 into TDMA bursts at a desired transmission car- rier frequency and supplied to the transmitting antenna 24. Correspondingly, a TDMA signal received by the re¬ ceiving antenna 26 is supplied to the transceiver unit 210, in which it is demodulated from reception carrier frequency to base frequency, after which a detection, de-interleaving, channel decoding and deframing are performed in the frame unit 7, and subsequently, the received control and user data are supplied through the interface 12 to the PCM link 11. For the measurement of the receiving antenna 26, the base station comprises a measuring signal source 112, e.g. a signal generator, generating a radio fre¬ quency measuring signal to be used for the measurement of the condition of the antenna, the frequency of the signal corresponding to some of the normal reception frequencies of the receiver, preferably within the range 800 to 1000 MHz. The output 132 of the measuring signal source 112 is connected to the antenna line 27 by means of a switching unit 28 comprising an RF switch S2 and directional couplers 28A and 28B. The test operation is controlled by an opera¬ tion and maintenance unit 20 of the base station, which unit commands, through a control line 20A, the signal source 112 to generate a test loop in a predetermined test time slot and, through a control line 20B, the switch S2 to switch either to the directional coupler 28A or 28B. The directional coupler 28A directs the measuring signal towards the antenna 26 for a reflection measurement of the antenna. The directional coupler 28B directs the signal towards the receiver for a reference measurement of the antenna measurement. The OMU 20 also acts as a measuring unit re¬ ceiving a signal from the branching element 29 and mea¬ suring the magnitude of the signal. Alternatively, re¬ ceivers Rx may contain a measuring equipment, the mea- surement result of which is received by the OMU 20 through a line 20c. The procedure of antenna measurement is as follows. The OMU 20 gives the signal source 112 a test command, in consequence of which a measuring signal is looped during a time slot of an idle frame used for the testing to the switch S2, which responsive to the status of line 20B switches the measuring signal to the direc¬ tional coupler 28B, which sends the measuring signal directly towards the receiver. The OMU 20 measures the magnitude of the measuring signal and uses the measure¬ ment result as a reference value. Then the OMU 20 changes the status of line 20B, in consequence of which the switch S2 switches the measuring signal to the di¬ rectional coupler 28A. The OMU 20 measures the magnitude of a signal component reflected from the antenna 26. From these measurement values the OMU 20 then calculates a value indicating the condition of the antenna, which value is compared with stored alarm thresholds, and the alarm is given, if necessary. The RF sections of the reception side of a base station can be tested by sending to the receiving an¬ tenna during one or several time slots of the idle frame used for the testing a predetermined radio frequency test signal carrying predetermined digital data. In a preferred embodiment of the invention shown in Figure 8, the test signal is sent by a subscriber terminal MS or a particular testing apparatus STM simulating a sub¬ scriber terminal, which are indicated generally by the reference numeral 11. The MS/STM 11 may be under direct control of the base station (broken line 13) in such a way that the base station may initiate sending a test signal. The test signal is received normally by the re¬ ceiver unit 210 and processed normally in the frame unit 7. Additionally, the frame unit 7 calculates on the basis of the received and known test data a bit error rate indicating the condition of the receiver sections. The OMU 20 receives the calculated value via line 20C and gives the alarm, if the predetermined alarm thresh¬ olds are exceeded. The OMU 20 may further measure the level of the received signal and, if necessary, give alarms associated therewith. Also the RF sections of the transmission side can be tested, if the test signal is generated by the frame unit 7 and the transmitter unit 21 and sent via the antenna 24 to the MS/STM 11, which sends the test signal back to the receiver of the base station, where the measures described above will be taken. The figures and the description related thereto are intended only to illustrate the present invention. As to the details, the method and the apparatus accord¬ ing to the invention may vary within the scope of the attached claims.

Claims: Claims: 1. Method for measuring the condition of a base station in a TDMA radio system, in which are used TDMA channel structures according to ETSI/GSM recommendation 05.02, by means of test measurements performed in prede¬ termined TDMA time slots, c h a r a c t e r i z -e d in that the test measurements are performed in time slots of an IDLE frame of a channel structure TCH/F+ SACCH/TF and/or in time slots of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02. 2. Method according to claim 1, c h a r a c ¬ t e r i z e d in that the condition of a receiving an- tenna of a base station is monitored by test measuring, the test measuring comprising a transmission of a predetermined radio fre¬ quency test signal via an antenna line to the antenna during one or several time slots of said IDLE frame, a measurement of the magnitude of a measuring signal component reflected from the antenna and propa¬ gated along a predetermined measuring path, a transmission of the measuring signal directly towards a receiver along said measuring path during one or several time slots of said IDLE frame, a measurement of the magnitude of the measuring signal transmitted directly along the measuring path, a determination of the condition of the antenna on the basis of the ratio between these two measured signal magnitudes. 3. Method according to claim 1, c h a r a c ¬ t e r i z e d in that the test measurement comprises a transmission of known test data to a receiver of the base station on a radio channel during at least one time slot of said IDLE frame, a reception of said test data by the receiver of the base station, a determination of a bit error rate on the basis of said received test data and known test data. 4. Arrangement for measuring the condition of a receiving antenna of a base station in a TDMA radio system, in which are used TDMA channel structures ac¬ cording to ETSI/GSM recommendation 05.02, by means of test measurements performed in predetermined TDMA time slots, c h a r a c t e-r i z e d in that the arrange¬ ment comprises means (S2, 28A, 112) for sending a predeter¬ mined radio frequency test signal via an antenna line (27) to the antenna during at least one time slot of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or during at least one time slot of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02, means (20) for measuring the magnitude of a measuring signal component reflected from the antenna and propagated along a predetermined measuring path, means (S2, 28B, 112) for sending a measuring signal directly towards a receiver along said measuring path during one or several time slots of said IDLE frame, means (20) for measuring the magnitude of the measuring signal sent directly along the measuring path, means (20) for determining the condition of the antenna on the basis of the ratio between these two mea- sured signal magnitudes. 5. Arrangement for measuring the condition of a base station in a TDMA radio system using TDMA channel structures according to ETSI/GSM recommendation 05.02, by means of test measurements performed in predetermined TDMA time slots, c h a r a c t e r i z e d in that the arrangement comprises means (11) for sending a predetermined radio frequency test signal to a receiver (210) of the base station on a radio channel during at least one time slot of an IDLE frame of a channel structure TCH/F+SACCH/TF and/or during at least one time slot of an IDLE frame of a channel structure SDCCH/8 according to the ETSI/GSM recommendation 05.02, means (7a, 7b) for determining a bit error rate on the basis of test data received by the receiver of the base station and of the known test data. 6. Arrangement according to claim 5, c h a r ¬ a c t e r i z e d in that said means for sending a test signal comprise a subscriber station or a separate test station (11). 7. Arrangement according to claim 6, c h a r ¬ a c t e r i z e d in that the subscriber station or the test station are controlled by the base station to be tested. 8. Method according to claim 6 or 7, c h a r ¬ a c t e r i z e d in that said means for sending the test signal comprise transmitter sections (7a, 7b, 21) of the base station and that the subscriber station or the test station (11) acts as a repeater, which sends the test signal to the receiver sections (210) of the base station.

Inventors: KOIVU VESA, KOIVU, VESA
Applicants: KOIVU VESA, NOKIA TELECOMMUNICATIONS OY, KOIVU, VESA
Application year: 1994
Main classification: H04B17
IPC codes: H04B7, H04B17, H04W24